Multi-layer tube for conducting fuel in a motor vehicle

ABSTRACT

A motor vehicle fuel conveying multi-layer co-extruded tube ( 1 ) comprising at least an innermost first layer ( 2 ) of a polyamide resin (P9T) consisting of a dicarboxylic acid component and a diamine component, wherein 60÷100% of the dicarboxylic acid component is terephthalic acid and 60÷100% of the diamine component is selected from 1,9-nonanediamine and 2-methyl-1,8-octanediamine; an intermediate second layer ( 3 ) of polyamide 6 (PA 6); an intermediate co-polyamide (CoPA)-based tie layer ( 4 ); and an external fourth layer of polyamide 12 (PA12).

TECHNICAL FIELD

The present invention relates to a tube of polymeric material forconveying fuels under high pressure from a pump to an engine of a motorvehicle. In particular, the present inventions relates to a multi-layerstructure having excellent properties of resistance to permeation,intra-layer adhesion, heat and chemical resistance and impact resistancealso at low temperature.

STATE OF THE ART

As it is known, tubes of thermoplastic or elastomeric material,preferably made of a number of materials with different chemicalcomposition, are used for conveying fuels in motor vehicles. For safetyreasons, a multi-layer tube for gasoline and/or diesel fuel has to beimpermeable to vapours of gasoline and/or diesel fuel and resistant toboth high and low temperatures, as well as flame-resistant. Further, theenvironmental provisions recently come into force impose progressivelystricter limits, in particular as concerns the emissions of volatilehydrocarbons or the like from the fuel tank and the fuel line ducts.

Also, catching on is the use of alcohol gasoline, that is of gasoline towhich, with a view to reducing consumptions and obtaining an improvementof performances, an alcohol having a low boiling point is added, such asmethanol and ethanol, or an ether such as methyl-terbuthyl ether (MTBE).In the presence of such compounds, however, conventional polyamide-baseresins such as nylon 6 or nylon 11, which ensure nevertheless goodproperties of mechanical resistance and flexibility, do not fully meetpermeability requirements. Increasing the layer thickness would benecessary, which would result in a reduction of flexibility and in anundesirable increase of weight and costs. Further, in the presence ofalcohol fuels, the greater permeability is associated with a worseningof mechanical properties, in particular in terms of elongation at tearand cold impact resistance.

Further, over the past few years, maximum pressure and temperaturevalues, in both gasoline direct injection (GDI) and diesel engines, havebeen rising. In the light of that, it is preferable that the materialsused for the manufacture of tubes for conducting fuels be extremelyresistant to high temperatures, so as to guarantee satisfactoryperformances.

It is known from U.S. Pat. No. 6,989,198 to use a multi-layer structurecomprising at least a layer comprising nylon 11 and/or nylon 12 and alayer comprising a polyamide resin (nylon 9T) consisting of adicarboxylic acid component and a diamine component, with 60÷100% mol ofthe dicarboxylic acid component being a terephthalic acid and 60÷100%mol of the diamine component being selected from 1,9-nonanediamine and2-metil-1, 8-octanediamine.

Such a multi-layer structure shows very good properties of resistance topermeation, in particular against noxious hydrocarbons contained inalcohol gasoline. At the same time, such a multi-layer structure ensuresproperties of thermal and chemical resistance.

However, the multi-layer structure disclosed by U.S. Pat. No. 6,989,198shows elongation at tear values which are limited in the extrusiondirection, and which are even more limited and not satisfactory in thecross-wise direction. Further, the structure disclosed by U.S. Pat. No.6,989,198 shows a poor workability by elastic deformation of the ends ofa tube section.

The above mentioned limitations prove particularly critical during thestages of assembling, fitting insertion, etc. because under thoseconditions it is easy to cause the yield, or even the cracking of thematerials.

OBJECT OF THE INVENTION

It is an object of the present invention to provide a tube in plasticmaterial which is suitable for solving the above mentioned drawbacks andwhich can at the same time ensure low permeability and high resistanceto both low and high temperatures.

According to the present invention, there is provided a multi-layer tubefor conducting fuel (gasoline and/or diesel fuel) in motor vehicles,characterized in that it comprises at least:

-   -   a layer comprising a nylon 9T polyamide resin (P9T) consisting        of a dicarboxylic acid component and a diamine component,        wherein 60÷100% of the dicarboxylic component is terephthalic        acid and 60÷100% of the diamine component is a diamine component        selected from 1,9-nonanediamine and 2-methyl-1,8-octanediamine;    -   a layer of polyamide 6 (PA6);    -   a tie layer; and    -   a layer of polyamide 12 (PA12).

In particular, according to a preferred embodiment of the presentinvention, there is provided a tube consisting of an innermost layer ofnylon 9T, an intermediate layer of PA6, a tie layer of a co-polyamide(CoPA), and an external layer of PA12.

BRIEF DESCRIPTION OF THE DRAWING

For a better understanding of the present invention, it is now furtherdescribed with reference to the attached FIG. 1, which illustrates atransverse cross-sectional view of a multi-layer tube of Example 1according to the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

The manufacture of tube 1 in polymeric material is carried out accordingto a well known process, whereas the combination of materials selected,and the consequent properties thereof are innovative.

In particular, a tube 1 according to the present invention comprises atleast:

-   -   a first innermost layer 2 of P9T, having preferably a thickness        in the range 0.10 mm÷0.25 mm;    -   a second intermediate layer 3 of PA6, having preferably a        thickness in the range 0.20 mm÷0.30 mm;    -   a third intermediate tie layer 4 of a CoPA, having preferably a        thickness in the range 0.10 mm÷0.30 mm; e    -   a fourth external layer 5 of PA12, having preferably a thickness        in the range 0.35÷0.55 mm.

Preferably, the first innermost layer 2 consists of P9T.

For the innermost first layer 2 a nylon 9T polyamide resin is preferablyemployed, which is particularly suitable for manufacturing a layer witha permeation barrier function, e.g. P9T GENESTAR by KURARAY. A P9T resinproves particularly effective as a permeation barrier layer, inparticular against alcohol fuels and peroxides tending to form in thefuel tank and in the fuel line, especially during the periods of parkingof the motor vehicle. Particularly, a nylon P9T polyamide resin alsoensures excellent properties of resistance to diesel fuel additivatedwith biodiesel (e.g. B30, B100, RME, SME, F.A.M.E., which are very harshtowards rubbers and plastic materials in general). Further, a nylon 9Tpolyamide resin has interesting adhesion properties, which allow toeasily couple a layer of nylon 9T with another layer of a differentpolymeric material without needing to resort to an intermediate adhesivelayer.

Preferably, the second intermediate layer 3 is made of a PA6, morepreferably of a plasticized and impact modified PA6, even morepreferably of PA6 1024 JI by UBE®.

For example, a polyamide 6 may be used having a melting point comprisedbetween 210 and 230° C., a tensile strength at yield comprised between25 and 35 MPa, a tensile elongation at break greater than 150% and anIzod impact strength (notched; 23° C.) between 100 and 200 J/m. Inparticular, a polyamide 6 is used which has improved properties ofelongation at break, not only in the extrusion direction, but also inthe cross-wise direction, thus advantageously improving the diametralelastic deformation properties thereof. In use, in fact, the ends oftube sections are bound to undergo diametral elastic deformations inview of certain applications (e.g. if used with quick-connect fittings,in the case of cold fitting over connections, etc.) Under suchconditions, if the structure is not sufficiently elastic, the occurrenceof breakages is very likely.

Preferably, the third intermediate tie layer is made of a co-polyamide,more preferably of a PA6/PA12 co-polyamide, even more preferably ofPA6/PA12 7034 by UBE®. For example, a PA6/PA12 co-polyamide may be usedhaving a melting point comprised between 190 and 210° C., a tensilestrength comprised between 90 and 110 MPa, and a tensile moduluscomprised between 550 and 750 MPa.

Unlike more commonly used adhesives, e.g. polyethylene- orpolypropylene-based adhesives, a co-polyamide-base tie layer exhibitsadvantageous properties of resistance to high temperatures, and inparticular to temperature peaks during use. Further, the use of such aco-polyamide-base tie layer proves advantageous during the stages ofpre-moulding of the tube, which are generally carried out at relativelyhigh temperatures (above 100° C.). The properties of other materialswith a more limited resistance to high temperatures could, as a matterof fact, be negatively affected by the exposure to such hightemperatures during the tube manufacture itself.

Preferably, the fourth external layer is of a PA12, more preferably animpact- and thermal-resistance-modified, plasticized PA12, even morepreferably is PA12 3030 JI26L by UBE®.

For example an impact-modified, plasticized PA12 may be used, having amelting point comprised between 170 and 180° C., a tensile strength atyield comprised between 25 and 35 MPa, flexural strength (ISO 178)comprised between 20 and 30 MPa, flexural modulus (ISO 178) comprisedbetween 400 and 600 MPa, an impact strength (Charpy, notched, ISO179/1eA) comprised between 100 and 120 kJ/m² at 23° C. and between 10and 20 kJ/m² at −40° C.

Commonly, the elastomeric and/or plasto-elastomeric materials used infuel-line tubes have limited thermal resistance, therefore they need tobe co-extruded with an external layer of a protective material, such asSunprene®. On the contrary, employing such a polyamide 12 allows for thedirect use within the engine compartment for operating temperatures upto approximately 150° C., without the need for a further externalprotective layer.

Alternatively, according to another preferred embodiment of the presentinvention, provided is a tube consisting of an innermost layer of nylon9T, an intermediate layer of PA6, a tie layer of a copolyamide (CoPA),an intermediate layer of PA12, and an external protective layer of amaterial consisting of a mixture of a polyamide and a functionalizedpolyolefin, wherein the polyamide is the matrix and which comprisesnanofillers. For example, such a material can be used having a meltingpoint comprised between 200 and 220° C., a flexibility (ISO 686standard) comprised between 25 and 50 Shore D and demonstrating creepresistance (ISO 899 standard) up to approximately 200° C. Preferably, amaterial of the X-LP series by Arkema® may be used.

The use of such a further external layer results in a furtherimprovement of thermal resistance (up to 180° C.) and provides themulti-layer structure with flexibility and improved resistance toabrasion (which is useful, for example, against the effect of rubbingwithin the engine compartment, etc.)

A tube according to the present invention can solve the drawbacks comingwith the tubes manufactured according to the prior art.

In particular, the structure of multi-layer tube 1 according to thepresent invention is suitable for use under conditions requiring a highresistance to gasoline, including gasoline containing differentpercentages of alcohols, and/ore resistance to diesel fuel and biodieselof RME, SME, F.A.M.E. type.

Further, the structure of the multi-layer tube 1 according to thepresent invention shows high resistance to hydrocarbon peroxides (e.g.Perox 90).

Permeability measurements have also shown that the structure of themulti-layer tube 1 according to the present invention ensures low fuelpermeation, in particular values of fuel permeation that are lower, orat least comparable with, those attained with the permeation barriermaterials commercially available.

The structure of the multi-layer tube 1 according the present inventionsfurther ensures a very wide operating temperature range, in particularan operating temperature range −50° C.÷140° C., with peaks at −60° C.and 150° C. With the multi-layer structures commercially available,operating temperature are normally in the range −30° C. (−40° C.)÷120°C., with peaks of approximately 125° C. (130° C.).

The multilayer tube 1 according to the present inventions showspronounced properties of impact resistance, also at low temperatures. Inparticular, cold impact resistance even at temperatures of about −60° C.makes the multi-layer tube according to the present inventionparticularly suitable for the use under climatic conditionscharacterized by very harsh winters, such as those typical of Russia(e.g. Siberia), of Arctic Countries, etc.

Further improvements with respect to multi-layer structures commerciallyavailable have been found in the multi-layer structure 1 according tothe present invention, in terms of elongation at tear, both in theextrusion direction and in the cross-wise direction. Also improved hasproved the workability by elastic deformation of the ends of a sectionof multi-layer tube according the present invention, which turns out tobe crucial in the stage of assembling fittings and connections, etc.

Further, while entailing an improvement in performances, the multi-layerstructure according to the present invention makes use of a smalleramount of nylon 9T with respect to a known nylon 9T/PA 12 bi-layerstructure, which results into a significant reduction of productioncosts.

Employing a co-polyamide-base tie layer further ensures properties ofresistance to high temperatures, which is particularly advantageousduring the pre-moulding of the tube.

Finally, modifications can be made to the multi-layer tube describedabove, in particular as concerns the layer thickness, without departingfrom the scope of the present invention. The invention will be describedby means of an example, but it is not however limited to it.

Example 1

A tube according the present invention has the structure and compositionshown in Table 1. Layers are numbered from the inside to the outside.

TABLE 1 Layer Material - Producer Thickness (mm) 1 P9T Genestar -Kuraray 0.15 2 PA6 1024 JI - UBE 0.25 3 PA6/PA12 co-polyamide 7034 - UBE0.10 4 PA12 3030 JI26L - UBE 0.50

Comparative Examples 2A-2D

Tables 2A-2D show structure and composition of tubes with which the tubeof Example 1 was compared. Layers are numbered from the inside to theoutside.

TABLE 2A Layer Material - Producer Thickness (mm) 1 ETFE AH3000 - UBE0.25 2 PA12 3030J16L - UBE 0.75

TABLE 2B Layer Material - Producer Thickness (mm) 1 PVDF KYNAR 720 -ARKEMA 0.10 2 ADHEFLON ASP 720- ARKEMA 0.05 3 PA12 RILSAN AESN P202 T6L-ARKEMA 0.85

TABLE 2C Layer Material - Producer Thickness (mm) 1 PA6 VESTAMIDBS0701 - DEGUSSA 0.45 2 EVOH EVAL FP101 - DEGUSSA 0.15 3 PA12-basedCoPA - DEGUSSA 0.10 4 PA6 VESTAMID LX9002 - DEGUSSA 0.30

TABLE 2D two-layer Layer Material - Producer Thickness (mm) 1 P9TGenestar - Kuraray 0.25 2 PA12 3030 JI26L - UBE 0.75

Permeability measurements were carried out according to a standardprocedure based on which, by means of successive weighings, theprogressive weight loss off a tube filled with a fuel under pressure (4bar) and kept at 60° C. is evaluated. Since the test circuit is closed,the loss weight is ascribable solely to fuel permeating through the tubewall and its subsequent emission into the surrounding environment.

TABLE 3 Example 1 Example 2A Example 2B Example 2C g/m²/h 3.51 4.11 4.215.83 L0003 FLUID g/m/24 h 1.59 1.86 1.90 2.64 L0003 FLUID g/m²/h 0.231.68 1.67 1.7 TF1 FLUID g/m/24 h 0.10 0.77 0.75 0.78 TF1 FLUID

Table 3 shows results of permeability measurements carried out on themulti-layer structure of the present invention and on different knownstructures commercially available. Data referring to 500 h of testscarried out at a constant temperature of 60° C. are expressed both interms of loss weight per surface unit per hour and in terms of lossweight per length unit over 24 hours.

Tests have been carried out by using as a test fluid respectively L0003(a diesel fuel additivated with 15% vol. methanol and 100 ppm of formicacid), known for its pronounced tendency to permeation, and TF1 (a fuelconsisting of 45% vol. toluene, 45% vol. iso-octane and balance 10%ethanol).

It will appear from the results that the tube according to the presentinvention shows the lowest permeation values under all conditionsconsidered, with a significant reduction of permeability.

TABLE 4 Example 2C Example 2B Example 2A Example 1 CM 15 g/m 98.0 82.130.6 5.3

Similarly, Table 4 shows the results of permeation tests carried out onthe multi-layer structure of the present invention and on differentknown multilayer structures, using as the test fluid a lab fuel (CM 15),consisting of 85% vol. Haltermann CEC-RF-08-A-85 (non-alcohol premiumunleaded gasoline, with 1.5% vol. maximum content of oxygenatedcompounds) and of balance 15% vol. methanol. Data referring to 500 htests carried out at a constant temperature of 40° C. are expressed interms of loss weight per length unit.

From the data of Table 4, it appears that the use of the multi-layerstructure according to the present inventions is associated with thelowest permeation value.

TABLE 5 Example 2C Example 2A Example 2B Example 1 CE 10 g/m 24.0 21.79.3 0.9Table 5 similarly refers to permeability tests carried out on themulti-layer structure of the present inventions and on different knownmultilayer structures, using as the test fluid a standard gasoline (CE10) (a gasoline containing 10% vol. ethanol). Data, referring to 500 htests carried out at the constant temperature of 40° C., are expressedin terms of weight loss per tube length unit.

In addition to permeability tests, tubes aged for 500 h at 60° C. weresubjected to mechanical tests so as to evaluate the effects oftemperature on impact resistance and elongation at tear, both in theextrusion direction and in the cross-wise direction, as well as to bursttests.

Also, mechanical tests were performed on tubes that had undergoneprolonged ageing at different temperatures. In particular, with themulti-layer structure according to the present invention (Example 1),surprisingly good results were achieved after ageing in alcohol gasolinefor 3000 h at temperatures of approximately 130° C.

As regards impact resistance, tests were carried out after ageing intest fluids, at temperatures in the range −40÷−60° C.

Table 6 shows some results referring to cold impact resistance testscarried out after 4 hours at −40° C. on tubes manufactured according toExample 1 that had previously aged in test fluids.

TABLE 6 Tube ageing prior to impact resistance test Test result After5000 h at 60° C. in CE 10 No cracks nor damages After 1000 h at 60° C.in CM 15 No cracks nor damages After 1000 h at 60° C. in Perox 90 Nocracks nor damages After 1000 h at 60° C. in L0003 No cracks nor damagesAfter 200 h of immersion in ZnCl₂ No cracks nor damages

Impact resistance tests were carried out at low temperature (−60° C.)after an ageing cycle of 3000 h, with internal flow of FAN B fluid at90° C. and pulsating pressure from 5.5 to 8 bar, external temperature of110° C. No cracks or damages were detected in the tubes.

The multi-layer tube according to the present invention was subjected toburst tests according to the SAE J2260 standard. Table 7 shows theresults of the tests carried out under different conditions andfollowing different ageing processes.

TABLE 7 Operating conditions Burst pressure (bar) Room temperature 79 At115° C. 37 After kinking 80 After 5000 h at 60° C. in CE 10 98 After1000 h at 60° C. in CM 15 79 After 1000 h at 40° C. in Perox 90 63

The multi-layer structure according to the present invention (Example 1)was subjected to elongation at tear tests. The test results of the areshown in Table 8.

TABLE 8 Example 1 - Example 1 - after 3000 h Example Measurement newageing 2 D - new Longitudinal 38.2-40.1 N/mm² 36.7-37.9 N/mm² 32.4-34.6N/mm² yield stress Cross-wise 40.7-41.9 N/mm² 41.1-42.8 N/mm² 34.8-37.4N/mm² yield stress Longitudinal 210-260% 210-226% 175-185% elongation attear Cross-wise 201-218% 205-212% 150-160% elongation at tear

During longitudinal elongation at tear tests a remarkable improvementwas reported with respect to a P9T/PA12 bi-layer structure (Example 2D).An even less expected and surprising result was achieved as regardscross-wise elongation at tear, for which a 150% improvement was recordedwith respect to a P9T/PA12 bi-layer structure (Example 2D).

In particular, the increased elastic deformability in the cross-wisedirection is advantageous in consideration of the use of quick-connectfittings for the assembly of tubes on a motor vehicle. With themulti-layer structure of the present invention, the occurrence ofbreakings at connection joints and fittings proved to be significantlyreduced.

1. A motor vehicle fuel conveying multi-layer tube comprising from theinside to the outside, at least: an innermost first layer comprising apolyamide resin (nylon 9T) consisting of a dicarboxylic acid componentand a diamine component, wherein 60÷100% of the dicarboxylic componentis terephthalic acid and 60÷100% of the diamine component is a diaminecomponent selected from 1,9-nonanediamine and2-methyl-1,8-octanediamine; an intermediate second layer of polyamide 6(PA6); a third layer consisting of a co-polyamide (CoPa)-based tielayer/ and an external fourth layer of polyamide 12 (PA12).
 2. The motorvehicle fuel conveying multi-layer tube according to claim 1, whereinsaid second layer comprises an impact modified polyamide
 6. 3. The motorvehicle fuel conveying multi-layer tube according to claim 1, whereinsaid polyamide 6 has a melting point comprised between 210 and 230° C.,a tensile strength at yield comprised between 25 and 35 MPa, a tensileelongation at break greater than 150% and an Izod impact strength(notched; 23° C.) between 100 and 200 J/m.
 4. The motor vehicle fuelconveying multi-layer tube according to claim 1, wherein said thirdlayer is a tie layer consisting of a PA6/PA12 co-polyamide.
 5. The motorvehicle fuel conveying multi-layer tube according to claim 1, whereinsaid PA6/PA12 co-polyamide has a melting point comprised between 190 and210° C., a tensile strength comprised between 90 and 110 MPa, and atensile modulus comprised between 550 and 750 MPa.
 6. The motor vehiclefuel conveying multi-layer tube (1) according to claim 1, wherein saidfourth layer comprises an impact- and thermal-resistance-ruodifiedpolyamide
 12. 7. The motor vehicle fuel conveying multi-layer tubeaccording to claim 1, wherein said polyamide 12 has a melting pointcomprised between 170 and 180° C., a tensile strength at yield comprisedbetween 25 and 35 MPa, flexural strength comprised between 20 and 30MPa, flexural modulus comprised between 400 and 600 MPa, an impactstrength (Charpy, notched) comprised between 100 and 120 kJ/m² at 23° C.and between 10 and 20 kJ/m² at −40° C.
 8. The motor vehicle fuelconveying multi-layer tube according to claim 1, wherein said firstlayer has a thickness in the range 0.10 mm÷0.25 mm.
 9. The motor vehiclefuel conveying multi-layer tube according to claim 1, wherein saidsecond layer has a thickness in the range 0.20 mm÷0.30 mm.
 10. The motorvehicle fuel conveying multi-layer tube according to claim 1, whereinsaid third layer has a thickness in the range 0.10 mm÷0.30 mm.
 11. Themotor vehicle fuel conveying multi-layer tube according to claim 1,wherein said fourth layer has a thickness in the range 0.35 mm÷0.55 mm.12. The motor vehicle fuel conveying multi-layer tube according to claim1, wherein said first, second, third and fourth layer are co-extruded.13. The motor vehicle fuel conveying multi-layer tube according to claim1, wherein it further comprises a fifth layer external to said fourthlayer, said fifth layer being of a material consisting of a mixture of apolyamide and a functionalized polyolefin, wherein the polyamide is thematrix, said mixture comprising nanofillers.
 14. The motor vehicle fuelconveying multi-layer tube according to claim 1, wherein said materialhas a melting point comprised between 200 and 220° C. and a flexibilitycomprised between 25 and 50 Shore D, said material further demonstratingcreep resistance up to approximately 200° C.
 15. The motor vehicle fuelconveying multi-layer tube according to claim 14, wherein said first,second, third, fourth and fifth layer are co-extruded.
 16. Use of amulti-layer tube according to claim 1, for conveying fuels of a motorvehicle.